Haematological and biochemical responses to training and overtraining

Abstract

Summary We sought a physiological marker of overtraining in horses, using commonly practised field and laboratory tests to allow early prediction and treatment of the syndrome. Thirteen Standardbred horses were trained as follows: phase 1 (endurance, 7 weeks), phase 2 (high intensity, 9 weeks) and phase 3 (overload, 18 weeks). In phase 3 the horses were divided into 2 groups: overload training (OLT) and control (C). The OLT group exercised at greater intensities, frequencies and durations than the C group. Overtraining occurred after 31 weeks and was defined as a significant decrease in treadmill run time to fatigue (RT) in response to a standardised exercise test (SET). Variables measured included: feed intake, bodyweight (BWT), resting haematology and plasma biochemistry and treadmill SETs to measure RT. The OLT group had a decrease in BWT after week 28 (P<.05) without a reduction in feed intake and a reduction in RT during the SET after 31 weeks. Signs persisted after 2 weeks of a reduced training load confirming overtraining. Haematology and biochemistry failed to detect any markers of overtraining. Although no physiological markers of overtraining were identified, empirical observations revealed that the behaviour of horses in the OLT group was different from those in the C group during the period of overtraining. This study reflects that a model of overtraining has been developed based on measurement of a reduction in performance; however, there were no consistent changes in haematology or serum biochemical values in association with the decrement in performance capacity.

Comparative Exercise Physiology

“…For example the mongrel dog has an HRmax of approximately 300 beats per minute (Wagner et al 1977) and the racing Greyhound 318 (Staaden 1984). The racing Thoroughbred or Standardbred horse can have an HRmax of 240 to 260 beats per minute (Tyler-McGowan et al 1999). In horses, HRmax also decreases with age, with HRmax of horses over 20 <200 bpm compared with approximately 220 bpm in their younger and middle aged counterparts (Betros et al 2002).…”

“…In a major review article on high intensity interval training in human endurance athletes, Laursen and Jenkins (2002) report the recent use of the velocity at which VO 2 max is achieved as the interval intensity. Tyler-McGowan et al (1999) also report value in this intensity for the aerobic capacity training of horses. Ideally, the velocity at VO 2 max should be tested fortnightly during interval training periods so that the interval training speed can be adjusted with improvements in aerobic function.…”

“…The velocity at which VO 2 max or HRmax is achieved may be selected as the goal interval speed. This intensity has been supported as the probable optimal training intensity for improving aerobic performance in both human studies (Laursen & Jenkins 2002) and horse studies (Tyler-McGowan et al 1999). It should be noted that reassessment of aerobic capacity is required at regular intervals, as the intensity needs to increase with improvements in VO 2 max.…”

Physiological Factors in the Interpretation of Equine Hematological Profile

“…In addition, there are no alterations in the proportions of the different WBC populations. Some overtrained horses develop eosinophenia together with clinical signs of disease, and this result has led to the hypothesis that EOSs may be a more sensitive indicator of training stress than other types of WBCs (Tyler-McGowan et al, 1999). It is important to take into account that decreased NEU count and later, increased LYM count is consistent with systemic or respiratory disease, that are common causes of loss of performance in trained horses (McGowan, 2008).…”

Biochemical abnormalities of athletic horses

“…46 Although the significance of increased plasma GGT activity in training racehorses is unclear, maladaptation to training might be suspected in athletic horses with plasma GGT activity approaching 100 U/L that also display weight loss, reduced performance despite continued training, and behavioral and appetite disturbances among other clinical anomalies. [46][47][48] Serum GGT should return to within reference limits if training intensity is decreased or training stopped. 2,46 Reduced hepatic function or other evidence of hepatic pathology has not been noted in athletic horses with mildly elevated plasma GGT activity, though mild elevations in serum bilirubin have been concurrently reported.…”